Drum dryers and revolving-roller flakers have been employed in industry for many years. They have been applied to a wide range of chemical products (organic and inorganic), pharmaceutical compounds, waxes, soaps, and food products.
Key to the performance of these machines is the maintenance of a controlled temperature distribution across the outside surface of the roller. The outside surface of the roller is the surface upon which the feed material to be dried or flaked is deposited. A common design objective is for this temperature distribution to be substantially uniform, or constant, from one endwall of the cylindrical roller to the other. Another common objective is that, if the temperature on the outside surface of the roller is to vary, it do so in a gradual fashion and by a relatively small amount.
A common design for drum flakers involves the use of a hollow cylindrical roller. Within the interior of the roller, and along its longitudinal axis, is placed a central pipe. The pipe is perforated with holes. A heat exchange fluid, such as water, is pumped transferred down the perforated central pipe. The fluid exits the central pipe through the numerous holes in a spray which strikes the inside surface of the roller. It is commonly observed that this cools the roller, which has been heated by the application of the heated molten feed material. A transfer of heat results (or the heat "flows") from the feed material to the roller wall (first to the outside surface then to the interior then to the inside surface) to the heat exchange fluid. The heat exchange fluid (now at an elevated temperature) then accumulates at the bottom of the substantially empty roller and is removed, commonly by means of a siphon line. See, e.g., U.S. Pat. No. 2,445,526; CHEMICAL ENGINEERS' HANDBOOK 11-40 to 11-41 (including FIGS. 11-26(c)-(d)) (Robert H. Perry & Cecil H. Chilton eds., 5th ed. 1973).
Another general approach has been to substantially fill the roller with heat exchange fluid, but to assure that good heat transfer and good subsequent mixing takes place by means of various baffling arrangements. See, e.g., U.S. Pat. No. 2,068,779; U.S. Pat. No. 3,633,663.
Only a few patents have employed a piping manifold to directly transfer a heat exchange medium directly to the inside surface of a heat exchange roller. U.S. Pat. No. 3,426,839
discloses a drum dryer design, which uses spoke pipes and longitudinal jet pipes to transfer gaseous steam from a central pipe to the roller wall. The longitudinal jet pipes are directly adjacent the inside surface of the roller, so that gaseous steam is distributed to the wall through tiny openings along the length of the jet pipe. The longitudinal jet pipes represented a good distribution mechanism for drum dryers employing gaseous steam.
U.S. Pat. No. 2,603,457 features the use of upwardly-directed jet injectors. This patent emphasizes quick withdrawal of the fluid, so that the hollow interior of the roller is never more than half full.
The present invention surpasses the prior art in that it provides an improved (and economic) temperature distribution across the outside surface of the heat exchange roller. In many cases, the desired temperature distribution is a uniform or only gradually varying one, and this invention is well adapted to generating these types of distributions.
It should be noted that the specification here provided simultaneously discloses both apparati and methods for exchanging heat. While it is anticipated that the present invention will primarily be used to effect flaking, as stated above, the apparati and methods here disclosed are well suited to other applications in other industries. Thus, for example, the invention is frequently referred to as either (a) a flaker or flaking machine, or (b) a heat exchanger. The latter designation is chosen to highlight that the instant invention includes non-flaking heat-exchange applications.